The "raw" hide that is removed from animals is only rarely processed immediately in a leather factory. Collecting and sorting the hides according to weight classes, compiling the "batches" and transporting the hides to the leather factory take at least a few days, often weeks or even months. Due to its protein content, untanned hide in its natural, wet state is a breeding ground for bacteria. In order to protect it from damage due to rotting, it must be preserved.
In order to prevent putrefactive bacteria from decomposing the hide substance, the simplest measure is to adequately reduce the water content in the hide. In tropical countries, the hides are air-dried. This requires a great deal of space and can only be carried out with small numbers of hides.
Usually, common salt is used for preservation; blood and dung are cleaned off the hides and they are either sprinkled with grains of salt or soaked for approximately 24 hours in a saturated saline solution. After the salt treatment, they are stacked on a slanted base so that the surplus brine can drain off; the hides are then bundled together. The water content of the hides drops from about 65% to about 40% as a result of the salt preservation step.
When the preserved hides are processed in the leather factory, the preservation salt is washed off with the waste water, which causes considerable water pollution.
For this reason, preservation has already been tried with an aqueous solution of sodium sulfide and acetic acid. However, the antimicrobial effect was not satisfactory.